DEFECT PRODUCTION MECHANISMS IN METALS AND COVALENT SEMICONDUCTORS

We discuss how defect production mechanisms in displacement cascades v ary according to the nature of the irradiated material. Our discussion is based on Molecular Dynamics (MD) simulation studies and reveal ver y different mechanisms for metals and covalent semiconductors. For met als we show how melting of the cascade core, in combination with long replacement collision sequences along low index crystallographic direc tions leads to the production of large number of defects in clusters a nd a small (approximate to 10%) fraction of isolated interstitials wel l separated from the cascade region. In silicon, we show how the energ y deposition process leads to the production of local amorphous region s and very few isolated Frenkel pairs. Because replacement collision s equences are extremely short in the open diamond lattice, very few or no isolated interstitials result. We argue that these observations pro vide a basis to understand the very large difference in freely migrati ng defect production efficiency in metals and silicon. The results pro vide an underlying cause for the extremely high bulk recombination eff iciency observed in ion implanted and annealed silicon and provide a p hysical basis for the ''+1'' interstitial model in ion implanted silic on.